Counterbalance mechanisms having means for adjustably tilting a load support surface or platform carried adjacent an upper end of a parallelogram linkage are known. U.S. Pat. No. 3,215,386 to Swensen teaches a tiltable seat pivotally attached to an upper frame member which is vertically movable relative to a lower frame member via a parallelogram linkage having pneumatic counterbalance means connected thereto. U.S. Pat. No. 4,729,533 to Hillary et al. discloses a monitor support including a tiltable platform connected to the upper end of a single parallelogram linkage, while U.S. Pat. No. 4,834,329 to Delapp discloses a monitor support including a tiltable platform connected to the upper end of a double parallelogram linkage. In the above constructions, the tilt angle or angle of orientation remains constant during vertical movement of the platform, and must be adjusted independently of vertical position.